Method of preparing non-woven fabrics



Nov. 22, 1966 R. c. HARRINGTON, JR 3,237,474

METHOD OF PREPARING NON-WOVEN FABRICS Filed Aug. 20, 1963 ROBERT C.HARRINGTON ,JR INVENTZR. mum

ATTORNEY-5 United States Patent C) 3,287,474 METHOD OF PREPARINGNON-WOVEN FABRICS Robert C. Harrington, Jr., Kingsport, Tenn., assignorto Eastman Kodak Company, Rochester, N.Y., a corporation of New JerseyFiled Aug. 20, 1963, Ser. No. 303,321 5 Claims. (Cl. 26425) Thisinvention relates to non-woven fabrics, and particularly to a method ofpreparing non-woven fabrics of high loft and low density.

Non-woven fabrics are often prepared from a commingled mass ofstructural fibers and heat fusible binder material. A web is firstprepared which is comprised of heat fusible binder material such asthermoplastic resin, in either fibrous form or particulate form, andstructural or base fibers. The heat fusible binder material issubstantially uniformly distributed throughout the web. The web is thenheated to fuse or melt the heat fusible binder material, and a multitudeof small molten globules are formed which tend to migrate to pointswhere two or more structural fibers make contact. Upon cooling, theglobules form bonds at the many points where they contact the structuralfibers.

Prior art heating methods have not always produced satisfactory bondingresults. Owing to the inherent heat insulating properties of theprepared web, it has been difficult to obtain satisfactory heat transferto the heat fusible binder material disposed within the interior portionof the Web. Thus, a substantial proportion of the heat-fusible bindermaterial in the interior of the web is either not fused at all or isinadequately fused and, as a result, does not perform its intendedbonding function. The exterior portions of the resulting non-wovenfabric are usually bonded to a satisfactory degree while the interiorportion is not and consequently, the structural fibers of which thenon-woven fabric is comprised are not uniformly bonded throughout.Pressure has been applied during heating or immediately thereafter in aneffort to overcome this non-uniform bonding of the structural fibers.The application of pressure is not desirable in the preparation ofbonded non-woven fibrous sheet material of high loft.

This invention is directed to a novel method of treating a web comprisedof structural fibers and heat fusible binder material whereby the heatfusible material is substantially all fused in a uniform manner andthere is produced a well bonded non-woven fabric or fibrous sheet ofhigh loft and low density, the bond strength being substantially uniformthroughout the fabric.

For a complete understanding of this invention reference is made to thefollowing detailed description and drawing, in which the single figureshows apparatus adapted for carrying out this invention.

In accordance with this invention an unbonded fibrous web comprised ofstructural fibers and a heat fusible binder material, either in fibrousform, particulate form, or both, and having a melting point .at leastabout 20 C. below the melting point of the structural fibers, isprepared by methods known in the art. Methods of forming an unbondedfibrous web are well known in the art and include carding, garnetting,air deposition, fluid paper making techniques and the like.

The prepared web is subsequently passed under or conveyed beneath aplurality of electrodes emitting visible high voltage dischargeshereinafter referred to as electrical sparks. The sparks pass throughthe fibrous web. The potential of the discharge is adjusted to provideelectrical sparks that possess sufiicient thermal characteristics so asto fuse or melt the heat fusible binder material disposed within theirpath. The electrical sparks pass 3,287,474 Patented Nov. 22, 1966 'icethrough the fibrous web to an electrode disposed on the side of the webopposite the discharge electrodes. The heat fusible binder materiallocated in the interior portion of the web and the heat fusible bindermaterial located on the exterior portion of the web opposite thedischarge electrodes are heated to substantially the same degree as theheat fusible material located at or near the surface of the web disposedon the side adjacent the discharge electrodes.

Referring to the drawing there is shown apparatus suitable for carryingout this invention. The apparatus is comprised of an endless conveyorbelt 10 adapted to convey a fibrous web 12 between a plurality ofdischarge electrodes 14 and lower electrode 16. The discharge electrodes14 are supported in spaced relation by means of electrically insulatingmember 18. The discharge electrodes are electrically connected to arotary contractor 20, which in turn is electrically connected to a highvoltage source 22. Endless conveyor belt 24 conveys the treated web awayfrom the treating area where it can be wound onto a mandrel, cut todesired lengths,

or otherwise handled for storage or subsequent shipment.

The apparatus shown in the drawing is adapted for continuous manufactureof bonded non-woven fibrous sheet material having high loft and lowdensity. In operation, an unbonded fibrous web comprised of structuralfibers and heat-fusible binder material, in fibrous form, particulateform, or both, having a melting point of at least about 20 C. below themelting point of the structural fibers is passed continuously betweendischarge electrodes 14 and lower electrode 16. Electric potential issupplied from high voltage source to rotary contractor which is rotatedat relatively high speeds by suitable means (not shown) such for exampleas a high speed motor. By means of the rotary contactor electricalsparks are intermittently discharged from all discharge electrodes 14.In traversing the gap or space between discharge electrodes 14 and lowerelectrode 16, the sparks pass through the moving fibrous web. The heatfrom these electrical sparks fuse the heat fusible binder material withwhich they make contact whereby a multitude of small molten globules areformed which migrate to points where a plurality of structural fibersmake contact and upon solidifying serve as a bond of these structuralfibers at this point. Owing to the fact that the electrical sparks passcompletely through the web substantially all the heat fusible bindermaterial with which they make contact is substantially uniformly heatedto its fusion temperature. The density of discharges per square inch canbe adjusted by known means and by so doing various degrees of bondingcan be obtained. More binder material will be fused, if a larger numberof electrical sparks are passed through the fibrous web therebyproviding for more bonding of the structural fibers.

It will be apparent that that portion of fibrous web 12 which has notpassed between the electrodes 14 and 16 is unbonded while that portionwhich has passed between electrodes is a bonded non-woven fibrous sheetmaterial of high loft and low density.

In operation of the apparatus above described suitable high voltage, lowamperage conditions are established during operation and can bealternating current potential or direct current potential. The potentialemployed will depend primarily on the thermal characteristics desired ofthe electrical sparks emitted from the discharge electrodes which, inturn, will depend on the melting point of the heat fusible bindermaterial employed and the melting point or decomposition temperature ofthe structural fibers. The potential will be high enough to supplyelectrical sparks of thermal properties sufi'icient to fuse the heatfusible binder material but not suificient to melt or otherwise affectadversely the properties of the structural fibers. It is well within theskill of those versed in the art, having before them the teachings ofthis invention, to adjust the potential to provide electrical sparks ofdesired thermal characteristics to melt or to fuse the specific heatfusible binder material employed. Potentials of from 5,000 to 50,000volts can be employed, pre-ferably under low amperage conditions of theorder of from about 10 milliamperes to 40 milliamperes.

Rotary contactor 20 insures that electrical sparks will be emitted fromeach of the electrodes. The number of electrodes employed will besufiicient to provide substantial coverage of the web to be treated. Theelec trodes can be spaced apart any desired distance, usually of theorder of from about 2 inches to 4 inches. The distance between the tipsof the discharge electrode and lower electrode will depend primarily onthe thickness of the web being treated. A distance of about 1 inch willprove satisfactory for ,42 inch thick webs and a distance of about 4 to6 inches will prove satisfactory for web of a thickness of about 2 to 4inches.

Structural fibers that are employed in preparing bonded non-wovenfabrics employing a heat fusible binder material as a bonding mediumtherefor, are preferably those having a melting point in excess of about20 C. of the melting point of the heat fusible material employed. Thestructural fibers can be the known synthetic resin fibers having thedesired melting point, natural fibers, and fibers prepared frominorganic materials. The structural fibers can vary in length from aboutA inch to as much as 8 inches or more. The preferred length in preparingnonwoven fabrics or fibrous sheet material is from about 1 inch to about3 inches. The denier of the structural fibers can be as great as about60 denier per filament, but for ease of handling and the greaterpliability, toughness, and the like of the bonded non-woven fibroussheet material prepared therefrom, it is preferred to use fibers of fromabout 1 /2 to 20 denier per filament. Mixtures of structural fibers canbe employed. Thus, for example, mixtures of two or more manmade fiberscan be used, mixtures of two or more natural fibers can be used, andmixtures of manmade and natural fibers can be used.

Natural fibers suitable for use as structural fibers include woolfibers, cotton fibers, silk fibers, asbestos fibers, and the like.

Artificial or manmade fibers suitable for use in the manufacture ofbonded non-woven fibrous sheet material include those prepared by knownmethods from synthetic resins such as the organic acid esters ofcellulose, specific examples being cellulose acetate, cellulosebutyrate, cellulose acetate propionate, cellulose triacetate, celluloseacetate butyrate and cellulose propionate; resins comprising copolymersof acrylonitrile such, for example, as a resin comprised of, by weight,10 parts of methyl acrylate and 90 parts of acrylonitrile, one comprisedof, by weight, 5 parts of vinyl acetate, 20 parts of vinylidene chlorideand 75 parts of acrylonitrile, and one comprised of, by weight, parts ofmethyl acrylate, 10 parts of methyl methacrylate, and 80 parts ofacrylonitrile; polyester resins such as the polyester derived from1,4-cyclovhexanedimethanol and terephthalic acid in accordance with themethod described in Patent 2,901,466, and polyethylene terephthalate;the polyamides such, for example, as nylon 6 (polycaprolactam), nylon6/6 (polyhexamethylene adipamide), nylon 6/ 10 (polyhexamethylenesebacarnide); polyolefins such as polyethylene and polypropylene; rayonor regenerated cellulose (cellulose xanthate) or often referred to asviscose; and the like.

The heat fusible binder material employed in carrying out this inventioncan be employed in either fibrous form or particulate form. If it isemployed in fibrous form it can be employed in lengths of from about A1.inch to 8 inches or more. The preferred length of fibers is from about 1inch to 3 inches. The denier of the potentially heat fusible bindermaterial can be as great as 60 denier per filament; however, for ease ofhandling and the like it is preferred to employ fibers having from about2 to 9 denier per filament.

As above set forth the choice or selection of the structural fibers willin most respects dictate the selection of the heat fusible bindermaterial to be employed in preparing the bonded non-woven fibrous sheetmaterial in accordance with this invention. The heat fusible bindermaterial should be selected so as to have a melting point of at leastabout 20 C. lower than that of the melting point or decomposition pointof the structural fibers employed. Suitable binder materials includepolyamides such as polycaprolactam, plasticized cellulose acetate,plasticized ethyl cellulose, saran, polyvinyl chloride, polyethylene,polyurethane, polystyrene, polyvinylidene cyanide, and the like.

The fibrous webs treated in accordance with this invention can becomprised of, by weight, from about 10% to 90% of structural fibers andfrom about 90% to 10% of heat fusible binder material.

The following examples are illustrative of this invention.

Example I A fibrous web having a Weight of 6 ounces per square yardcomprised of, by weight, rayon fibers (2 denier per filament, averagelength about 2 inches) and 20% polyethylene fibers (2 denier perfilament, average length about 2 inches) is passed through a dischargezone on apparatus similar to that shown in the single figure of thedrawing. The discharge electrodes are spaced apart from one anotherabout 3 inches. A direct current potential of about 20,000 volts at 30milliamperes is applied to the electrodes. The fibrous web is movedthrough the discharge zone at a speed of about 10 feet per minute andthe rotary contactor is operated at a speed sufiicient to provide 1000electrical discharges per minute. A well bonded nonwoven fibrous sheetis produced which retains its initial loft and is bonded to the extentthat it can be processed through the normal operations required to formquilted articles without destroying its bonded identity.

Example II A fibrous web having a weight of 5 ounces per square yardcomprised of, by weight, 70% of polyester fibers (2 denier per filament,average length 2 inches) and 30% polyethylene fibers (2 denier perfilament, average length 2 inches) is prepared. The polyester fibers areprepared from the resinous condensation product of1,4-cyclohexanedimethanol and terephthalate acid in accordance with themethod described in Patent 2,901,466. These fibers are availablecommercially under the proprietary designation Kodel. The web is treatedin a manner similar to that of Example I with the exception that apotential of 25,000 volts at 20 milliamperes is used and the rotarycontactor is rotated at a speed to give intermittent discharges at arate of about 1,500 per minute. The web is moved through the dischargezone at a speed of 15.

feet per minute. A Well bonded non-woven fibrous sheet of high loft andlow density is produced. The bonded non-Woven fibrous sheet resistsdeformation and destruction when put through any of the normal processesfor forming quilted articles.

Example III A fibrous web having a weight of 4 ounces per square yardcomprised of, by weight, 60% polypropylene fibers (2 denier perfilament, average length about 2 inches) and 40% polyethylene fibers (2denier per filament, average length about 2 inches) is prepared. Thisweb is treated in a manner similar to that of Example I with theexception that a potential of 30,000 volts at 10 milliamperes is usedand the rotary contactor is operated at a speed sufficient to provideintermittent discharges at a rate of about 2,000 per minute. The fibrousweb is moved through the discharge Zone at a speed of about 20 feet perminute. A well bonded non-woven fibrous sheet is prepared which shows abreak strength in the machine direction of three pounds on a 1 inch widestrip and an elongation of about 80%. A bonded non-woven fibrous sheetprepared by prior art heating methods has only a 4 pound breakingstrength and a elongation on a same size sample.

Example IV A carded web of rayon is dusted with 20% of its weight ofpolyethylene powder and treated in a manner similar to that used inExample I, with the exception that a potential of 30,000 volts atmilliamperes is applied to the electrodes and the rotary contactor isoperated at a speed sufficient to provide intermittent discharges at arate of about 1,000 per minute. The web is moved through the dischargezone at a speed of about 10 feet per minute. The resulting product is afirmly bonded nonwoven fibrous sheet having its original low density.The member has adequate strength and elongation to carry it through allprocessing operations required for the manufacture of insulated weavingapparel.

Bonded non-woven fibrous sheets prepared in accordance with thisinvention have sufficient tensile characteristics that they canwithstand not only use, but also and more dry cleanings or washingswithout losing their bonded identity.

It is to be understood that the above description and drawing areillustrative of this invention and not in limitation thereof.

I claim:

1. A method of preparing a bonded non-woven fibrous sheet comprising thesteps of forming a heat fusible binder material and fibers into a mat,placing said mat between at least two high voltage electrodes, andproducing high voltage electrical sparks between said high voltageelectrodes and through said web thereby inducing internal heating ofsaid web so that the heat fusible binder material is cured thusproducing a bonded non-woven fibrous sheet.

2. A method in accordance with claim 1 wherein the thermal energy ofsaid high voltage electrical sparks is sufficient to fuse said heatfusible binder material without affecting adversely the properties ofsaid fibers.

3. A method in accordance with claim 2 in which said fibers in said mathave a melting point in excess of about 20 C. of the fusing point ofsaid heat fusible binder material.

4. A method in accordance with claim 3 in which said heat fusible bindermaterial is polyethylene.

5. A method in accordance with claim 1 wherein the mat is continuouslypassed between said high voltage electrodes.

References Cited by the Examiner UNITED STATES PATENTS 2,324,838 7/1943Harz.

2,331,321 10/1943 Heaton.

2,406,714 8/1946 Strickland 26426 2,433,412 12/1947 Hacklander 21910.612,476,283 7/1949 Castellan 264-26 2,497,117 2/1950 Dreyfus.

2,796,912 6/1957 Bartose 219-.053 2,822,575 2/1958 Imbert.

3,081,485 3/1963 Steigerwald 219-10.61

ROBERT F. WHITE, Primary Examiner. R. B. MOFFITI, Assistant Examiner.

1. A METHOD OF PREPARING A BONDED NON-WOVEN FIBROUS SHEET COMPRISING THESTEPS OF FORMING A HEAT FUSIBLE BINDER MATERIAL AND FIBERS INTO A MAT,PLACING SAID MAT BETWEEN AT LEAST TWO HIGH VOLTAGE ELECTRODES, ANDPRODUCING HIGH VOLTAGE ELECTRICAL SPARKS BETWEEN SAID HIGH VOLTAGEELECTRODES AND THROUGH SAID WEB THEREBY INDUCING INTERNAL HEATING OFSAID WEB SO THAT THE HEAT FUSIBLE BINDER MATERIAL IS CURED THUSPRODUCING A BONDED NON-WOVEN FIBROUS SHEET